(1) Field of the Invention
The present invention relates to a sound absorbing muffler for silencing the exhaust of a compressed air driven motor.
(2) Description of the Related Art
Sound absorbing mufflers of the type provided by the present invention are commonly used on reciprocating air motors that drive reciprocating fluid pumps. Generally, these types of air motors comprise a cylinder housing containing a reciprocating piston. A piston rod extends from one end of the cylinder housing and is connected to the reciprocating pump. A valve mechanism alternately supplies compressed air to opposite sides of the piston of the motor to reciprocate the piston and the piston rod extending from the cylinder housing of the air motor. The reciprocating movement of the piston rod drives the reciprocating pump. The valve mechanism and the piston of the air motor are both lubricated with grease and/or oil.
The air motor and pump assembly of this type is frequently used in confined work areas where the amount of available space for accommodating the air motor and the pump is very limited. In such an environment, the muffler of the air motor must be large enough to contain sufficient sound absorbing material to adequately silence the exhaust of the air motor. However, the muffler cannot be so large that it interferes with the installation of the air motor and pump in the intended working environment.
Another disadvantage associated with the larger prior art mufflers is that they protrude from the housing structure of the air motor. These larger mufflers at times protrude from the operative environment of the air motor and pump into an adjacent work area where they can come into contact with other machinery and be damaged or prevent their installation altogether.
The optimum air motor muffler would be as small and inobtrusive as possible, while adequately silencing the exhaust of the air motor. However, these are not the only characteristics considered in developing the optimum air motor muffler design. For example, in order for the muffler to adequately silence the exhaust from the air motor, it may be necessary to pass the exhaust through a sound absorbing material contained in the muffler. Some materials known for their sound absorbing properties that have been used in some air motor mufflers and in applications other than mufflers for air motors include sintered powdered metal, open cell plastic, corrugated paper, glass fiber, and foam rubber. During operation of the air motor however, it is possible for some of the grease and oil lubricating the valve mechanism of the air motor, and some condensed water that will often be supplied to the air motor along with the pressurized air, to be exhausted along with the air motor exhaust into the muffler. This creates the problem that the grease, oil or water exhausted from the air motor will not pass through some sound absorbing materials, but will be trapped in and absorbed by the sound absorbing material contained in the muffler. This could cause the material to swell up as it absorbs the grease, oil or water, and cause the pores of the material to decrease in size or clog due to small pore size, resulting in a decrease in the overall porosity of the sound absorbing material. This is especially true of foam rubber, one of the most efficient materials at absorbing sound. The decrease in the porosity of the material from the absorption of the grease, oil or water carried by the air motor exhaust will increase the resistance of the material to the flow of exhaust through the material. This, in turn, will decrease the efficiency of the air motor operation and cause increasing amounts of grease, oil and water exhausted from the air motor to be trapped in the muffler. In addition, should foam rubber or a similar spongy material be used as the sound absorbing material in the muffler, as the material absorbs increasing amounts of grease, oil and water exhausted from the air motor, the resistance of the material to the flow of exhaust through the material increases. The material's increasing resistance to exhaust flow causes the exhaust supplied to the muffler to exert an increasing compressive force on the material. In spongy materials, this tends to compress the clogged material and further decreases its porosity. The further decrease in the material's porosity results in a further increase in the resistance of the material to the flow of exhaust through the material, and a further decrease in the efficiency of the air motor's operation.
Although there is a need for an air motor muffler having reduced physical dimensions to avoid the drawbacks of interfering with the installation of the air motor and pump assembly in its intended working environment, there are also drawbacks involved in limiting the size of the muffler. These drawbacks include the corresponding reduction in the amount of sound absorbing material that can be used in a smaller muffler and its effectiveness in silencing the exhaust of the air motor, and the increased likelihood that grease, oil or water exhausted from an air motor will clog the reduced volume of sound absorbing material. In order for a small volume of sound absorbing material to absorb the sound of a larger volume of sound absorbing material, the number of pores per unit volume for the small volume must be increased. Correspondingly, with an increase in the number of pores per unit volume, the size of the pores must decrease. This increases the number of exhaust flow pathways through the material, but decreases the size of the pathways. Should a material similar to the previously listed materials be used as the sound absorbing material in the air motor muffler (e.g. sintered powdered metal, open cell plastic, corrugated paper, glass fibers, foam rubber) the decreased pore size would result in an increased likelihood that grease, oil or water exhausted into the material will clog the pores, and/or will cause the material to swell, further decreasing the pore size and restricting exhaust flow through the material. As described earlier, should a pad of foam rubber, a very efficient sound absorber, be used in a smaller muffler as the sound absorbing material, as it begins to clog and resist exhaust flow through the pad the force of the exhaust on the pad will tend to compress the pad. This compression will, in turn, further restrict the flow of exhaust through the pad.
It is therefore an object of the present invention to achieve the aim of reducing the physical dimensions of a muffler for an air driven motor, while also overcoming the drawbacks of the reduced volume of sound absorbing material absorbing less sound and restricting the flow of exhaust through the material. The objectives are achieved by providing a muffler with a substantially reduced size that permits it to be incorporated into the housing of the air motor and does not interfere with the installation of the air motor and pump assembly in its working environment. The muffler housing contains features that enhance the unrestricted flow of exhaust through the muffler. The muffler contains a pad of sound absorbing material that, despite its reduced size, adequately absorbs sound and conforms to noise standards set by OSHA with an added factor of safety. The pad does not restrict the flow of grease, oil or water exhausted into the material from passing through the pad, and does not appreciably swell or absorb the grease, oil or water exhausted into the pad. The pad material is also semi-rigid, and contributes to avoiding any compression due to high exhaust pressure which would decrease the pore size of the pad should a portion of the pad become clogged.